The present invention relates to a method for removal of a hydrate plug. More specifically it relates to a method for removal of a hydrate plug in a tube in connection with a petroleum well where the method comprises to provide a wireline tractor provided with a collecting container. The invention also comprises a device for performing the method.
Under unfavorable conditions in tubes in connection with petroleum wells, so-called hydrate plugs may be formed. Hydrate plugs are constituted of a material similar to wax, which may be dissolved by means of heat or by means of a hydrate dissolving fluid, for example methanol or monoethylene glycol.
Hydrate plugs are often formed relatively high up in well systems. Wells on the seabed are especially exposed because of the relatively low temperature there.
It might be quite complicated to get access to hydrate plugs, especially in wells where the well completion takes place on the seabed. In order to dissolve hydrate plugs in such wells, it may be necessary to use a vessel for the well intervention.
Circulation of hydrate dissolving fluid by means of a coil tubing has shown to be efficient in the removal of hydrates. However, the method requires rigging up of a considerable amount of device and thus is both time consuming and expensive.
It is also known to displace a heating element down to the hydrate plug in order to melt it. However, prior art in this field is not efficient and melting of the hydrate plug thus uses disproportionately much time. The patent WO2011/145950 discloses such a method.
Patent WO03/036020 discloses a wireline tractor provided with a collector and a scraping device. The wireline tractor is displaced to where sand and other deposited impurities completely or partially block the passage in a tube. The scraping device pulls loose the material and the loosened material is thereafter moved into the collector. The wireline tractor with the collector is brought to the surface and the collector is emptied. This is done by having the wireline tractor taken out of a sluice. The scraping device is not suitable for pulling of hydrate from a hydrate plug.
A method comprising a wireline tractor has the advantage of being carried out by means of light intervention devices.